
The total energy consumption of all users is formulated for an uplink NOMA-based MEC network via optimizing transmission power, offloading data and time allocation.
Different from [1]} and [2]}, time allocation for different groups is investigated in this paper, where two users are paired in each group to perform NOMA.

The total energy minimization problem is proved to be a convex one.
Besides, it is also shown that transmitting with maximal time is optimal in energy saving.

Based on the optimal conditions, an iterative algorithm is accordingly proposed, where closed-form expressions are obtained in each step for optimizing time allocation or offloading data.
The proposed iterative algorithm with low complexity is successfully proved to be globally optimal.

